Rough Running Johnson GT 150

[DjKoKo]

J150stlcos

I'm thinking I'm narrowing it down but I'm going to give this a shot and see how close I am.

Fresh fuel in the tank - New Fuel/Water Separator, primer bulb. - Compression test is fine.

(on the muffs) I primed the bulb and fired up the motor with No problem. It ran ok but I notice a slight hiccup every 2-4 seconds. it will rev up a little and come back down on it's own as well.

( in the Water) I tried to see what it would do in the water and same thing as on the muffs. BUT when I went to put it in gear it sputtered even worse. I tried to give it higher throttle and it wanted to but it kept sputtering. I loaded it back on the trailer and went home.

Tonight I fired it up again and after about 60 sec it killed. It took a few seconds to get it started back up again but I got it running like before with the slight hiccups. I reved it up on when I brought the throttle down, it killed again. both times it killed the primer ball was empty and I had to squeeze it back up.

I'm thinking Carbs and Maybe a bad pickup. I want to try to run fuel straight from a gas can and bypass the primmer bulb and separator.

Any suggestions??? or other test??? I'm all ears.

 

[emdsapmgr]

Re: Rough Running Johnson GT 150

Your primer bulb sounds normal. The primer bulb should get hard when you pump it up. Once running-the bulb will soften up, but should not collapse. You may have a lean sneeze on the engine. A miss every few rpm. This is a carb problem. A lean condition due to fuel restriction/debris in the idle passages in the upper carb bodies. When idling, the carb butterflys are closed. All fuel must pass through special dedicated fuel passages/circuits. Once you crack the throttle a little, the carbs will get fuel from the other two jets and may run fine on top end. You probably need to overhaul the carbs and pay close attention to getting the restriction (dried fuel) out of the idle circuits. The engine idle should be 650-750 rpm, set when the engine is in gear and the boat is floating at normal level in the water. Just in case, you might want to take a fuel sample from the tank just to make sure you don't have any water contamination.

 

[jonesg]

Re: Rough Running Johnson GT 150

Sounds like lean sneeze.
Carb rebuild with carb kits.

Good move bringing it home when it wouldn't run right, lots of guys force the issue and melt a piston.

I bought a 150hp with unknown service history.
My mechanic gave me a list like of work I needed to do before he'd test run it for me.
REbuild carbs,
change gear oil,
remove prop and clean shaft,
change fuel filter.
Drain tank,
replumb hoses,
water pump,
check anodes,
decarb with seafoam.
Clean all elec terminals
check fuse
test alarms
clean oil tank and fill with fresh oil
top up Tilt/trim reservoir
etc etc

Needless to say it ran pretty good after that.

When read posts where a newbie buys a boat and immediately runs the snot out of it.... all it takes is a tiny bit of junk in a carb to permanently kill the engine.